The invention relates to an apparatus and method for melt spinning a synthetic yarn.
EP 0 682 720 and corresponding U.S. Pat. No. 5,976,431 disclose a melt spinning apparatus and method wherein freshly extruded filaments are advanced in a cooling tube with a vacuum atmosphere. The cooling tube is arranged at a distance from the spinneret, so that an air stream develops in the cooling tube for cooling the filaments in the direction of the advancing yarn. In this connection, the flow velocity of the air and the spinning speed are adapted to each other such that the air stream assists the filaments in their advance in the cooling tube. With that, it is accomplished that the solidification point of the filaments moves away from the spinneret. This leads to a delayed crystallization of the polymer that favorably influences the physical properties of the yarn. Thus, for example, in the production of POY yarn, it was possible to increase the withdrawal speed and, thus, the draw ratio, without changing the elongation values necessary for further processing of the yarn.
The known spinning apparatus consists of a cooling tube and a suction device downstream of the spinneret. Between the spinneret and the cooling tube, an inlet cylinder extends with a gas permeable wall. By the interaction of the inlet cylinder and the suction device, a quantity of air is introduced within the spin shaft and guided within the cooling tube as an accelerated air stream in the direction of the advancing yarn. As the filaments pass through the inlet cylinder, they are precooled in such a manner that an increase of viscosity in the surface layers causes the firmness of the surface layer to increase. Upon their entry into the cooling tube, the filaments are still molten in their core, so that final solidification occurs only in the cooling tube. To this end, the cooling tube consists of a funnel-shaped inlet with a narrowest cross section in the cooling tube and cylindrical portion directly adjacent thereto. The narrowest cross section and the cylindrical portion cause the air stream to accelerate such that the filaments are assisted in their advance and undergo a delayed solidification only in the cooling tube. However, in the case of coarser filament deniers, the problem arises that while the air stream entering the cooling tube assists the advance of the filaments, it will not lead to an adequate cooling of the filaments. Although the known spinning apparatus is provided with an air supply device at the inlet end of the cooling tube for generating an additional cooling stream, same leads, however, to a considerable cooling of the filaments already before the air stream is accelerated in the cooling tube, so that the positive effect of a delayed crystallization of the polymer is not effective or only inadequately effective.
It is therefore an object of the invention to improve the initially described spinning apparatus and method such that filaments with coarser deniers are adequately cooled over a short distance, even in the case of delayed crystallization of the polymer, and at high spinning speeds.
The above and other objects and advantages of the invention are achieved by the provision of a melt spinning apparatus and method which includes an extruder for heating a polymeric material and extruding the resulting melt through a spinneret nozzle to form a plurality of downwardly advancing filaments. A cooling tube is disposed below the spinneret nozzle and comprises an inlet, a cylindrical portion below the inlet, and an outlet. A gas permeable inlet cylinder is positioned between the spinneret nozzle and the inlet of the cooling tube, and a suction generating device is connected to the outlet of the cooling tube so as to generate an initial cooling air stream through the cooling tube in the direction of the advancing filaments. An air supply device is provided for generating an additional cooling air stream in the cooling tube, with the air supply device being positioned downstream of the inlet of the cooling tube. Also, guide means is provided for gathering the advancing filaments to form an advancing multifilament yarn, and a winder serves to wind the advancing multifilament yarn into a package.
The invention has the advantage that the initial air stream present at the inlet end of the cooling tube serves to delay exclusively crystallization of the polymer. This ensures that the solidification point of the filaments is inside the cooling tube. For further cooling of the filaments, use is made of the additional cooling air stream that is introduced by the air supply device. To this end, this air supply device is arranged downstream of the narrowest cross section of the inlet in the cylindrical portion or downstream of the outlet end of the cooling tube. With that, it is accomplished that the additional cooling air stream contacts the filament bundle only shortly before or after solidification of the filaments. This influences in particular the evenness of the filament cross sections and results in a high spinning reliability and absence of lint.
In one preferred embodiment, the air supply device connects to the cooling tube so that the additional cooling air stream and the initial cooling air stream flow together in the direction of the advancing filaments. Since the two air streams are equidirectional, turbulence is essentially avoided.
In this connection, it is possible to construct the air supply device in a simple manner by an opening in the wall of the cooling tube. The cooling stream entering the cooling tube through the opening adjusts itself automatically due to the vacuum atmosphere in the cooling tube.
A further development of the invention provides that the air stream entering at the inlet end of the cooling tube and the additional cooling air stream entering the cooling tube through the opening are adjustable independently of each other. To this end, the air supply device comprises an air stream generator that generates the additional cooling air stream. The air stream generator could be, for example, a blower.
In a particularly advantageous embodiment of the spinning apparatus, the air stream generator is constructed as an injector with a nozzle bore that connects to a source of compressed air. In this arrangement, the nozzle bore of the injector terminates directly in the opening in the wall of the cooling tube. Also, the center axis of the cooling tube and the nozzle bore form an acute angle in direction of the advancing yarn, so as to introduce into the cooling tube the additional cooling air stream so as to have a directional component in direction of the advancing yarn. Such a configuration of the spinning apparatus is also suitable in particular for threading the filaments into the cooling tube at the start of the process. An angle range from 15xc2x0 C. to 30xc2x0 C. further provides that in the region of the cooling air stream the filament bundle is safely kept off the wall of the cooling tube.
To adjust the cooling air stream as a function of the filament type and filament denier, the free flow cross section of the opening may be adjustable by means of a sleeve mounted on the cooling tube, and which is arranged for movement along the cooling tube for closing the opening in full or in part.
In an advantageous further development, the adjustment device may comprise an air chamber enclosing the opening in the cooling tube on the outside. This air chamber has a supply line with a throttling device. Thus, it is possible to control the air supply to the air chamber by means of the throttling device in the supply line.
To achieve with the cooling stream a most intensive possible cooling, it is possible to connect the supply line of the air chamber to the air stream generator.
In the above embodiments, the opening arranged in the wall of the cooling tube may be made as a bore or a radial cutout. In a particularly advantageous further development of the spinning apparatus, the opening is formed by an annular, perforated sheet element in the wall of the cooling tube. In this instance, the perforated sheet element extends about the entire circumference of the cooling tube. This ensures a uniform inflow of the cooling air stream into the cooling tube. The plurality of holes permits a flow to be generated that has little turbulence.
The perforated sheet element may be made conical with a cross section increasing in direction of the advancing yarn and arranged in the extension of the cooling tube at the outlet end thereof. With that, cooling of the filaments is further intensified since the expansion of the air stream effects a better mixing between the initial cooling air stream and the additional air stream.
Besides a very intensive cooling, a particularly advantageous further development facilitates a preliminary drawing of the filaments. Here, the additional cooling air stream is oppositely directed to the direction of the advancing yarn and generates on the filaments a frictional force that acts against the direction of the advancing yarn. This frictional force effects a drawing of the filaments.
In another embodiment, the air supply device is constructed such that the suction device can generate the additional cooling air stream. To this end, a second cooling tube connects as an extension to the first cooling tube directly to the outlet chamber of the suction device.
To equalize the flow, it is preferred to construct the second cooling tube with a funnel-shaped inlet and a cylindrical outlet with an air-permeable wall.
To increase the draw effect in the case of such an air supply device, the cooling tube could include a heating device.
The method of the present invention is characterized in particular in that it permits production of textile or industrial yarns of polyester, polyamide, or polypropylene with coarse deniers and high elongation values. The method may be coupled with different treatment devices, so that, for example, fully drawn yarns, partially oriented yarns, or highly oriented yarn can be produced.